It has been argued that most Y chromosome coded genes are likely to have roles in sperm production or function. However, it is not clear if these genes provide essential spermatogenic function or just potentiate the spermatogenic process. The goal of this application is to determine the minimum Y chromosome gene requirement that is compatible with successful reproduction by assisted reproductive technologies (ART). The hypothesis of this application is that a Y gene complement of as few as two or three genes is enough to enable the production of male `gametes'(round spermatids or sperm) that are capable of participating in fertilization if delivered into the oocytes via injection. In preliminary data we provide evidence that in the mouse the presence of only two Y-coded genes, Sry and Eif2s3y, allows formation of testes, ongoing spermatogonial proliferation, and completion of meiosis to generate round spermatids. We suggest that further addition of one copy of Zfy is sufficient to allow the production of some sperm, albeit with morphologically abnormal heads. We also show that assisted reproduction by ICSI and IVF enable the generation of live offspring from subfertile and infertile males with Y chromosome deficiencies. In this application we will focus on analyzing various mouse models with limited Y gene complements: (1) males with an almost intact Y short arm but complete absence of Y long arm genes;(2) males with no Y long arm genes and the known Y short arm genes limited to Sry, Eif2s3y, a single copy of Zfy, and a reduced number of copies of Rbmy;and (3) males with only Eif2s3y and Sry. In Specific Aim 1 we will generate these males with limited Y gene complements and define more precisely at what stage of spermiogenesis cells arrest or become abnormal. We will perform histological analysis of the testes, confirm the presence of specific spermatogenic cell types by immunostaining, and examine acrosome development as a marker of spermiogenic stage. In Specific Aim 2 we will use sperm and/or round spermatids from these models for ICSI and/or ROSI. We will observe early post-fertilization events after injection, obtain embryos, and produce live offspring. We will genotype progeny to test which sperm genotypes were successful in supporting fertilization and embryo development. The significance of this application is that it will advance the understanding of the role of Y chromosome encoded genes in spermatogenesis and sperm function;it will also provide valuable information for those using ART to treat human infertility associated with Y gene deficiencies. PUBLIC HEALTH RELEVANCE: In this application we seek to determine the minimum Y gene complement that is compatible with the generation of sperm competent in fertilization via ART (ICSI and ROSI). The study will add to the understanding of the functions of Y chromosome coded genes by defining which Y genes provide essential spermatogenic function rather than just potentiating the spermatogenic process. The application also has significance for those utilizing ART to treat male infertility.